7 
metry for small-scale maps will develop in the direction of small-scale photography. It is 
desirable to carry out systematic research work and fortunately comm. E of the 
O.E.E.P.E., which so far could not make much progress because of lack of good photo- 
graphy, now starts with its experiments of interpretation of photographs in the scale 
1 : 125,000 for a map 1 : 100,000. Before discussing other problems of photogrammetric 
exploitation of these small-scale photographs, it will be necessary to answer the question 
whether this kind of photography can be used for other purposes than the production of 
topographic maps in the scale 1 : 250,000, 1 : 100,000 and even 1 : 50,000. 
The first answer is that they can be used for geological interpretation. So far the 
scale of most of the geological mapping has been between 1:40,000 and 1l: 60,000. Àn 
advantage of a smaller scale is that the coverage of each model is larger. In Delft very 
good results were obtained with the geological interpretation of trimetrogon oblique 
photographs of mountainous terrain. This experience promises good results for the use 
of the super Aviogon photographs for the same purpose. However, also for this type of 
work the 8096 longitudinal overlap will be necessary. 
For vegetation maps and for forestry this scale is too small and will show no more 
than a distinction between forested and non-forested areas. 
The result of these considerations is that the small-scale photographs between 
1:70,000 and 1:100,000 can only be used for topographic mapping and for geology. 
For agriculture and for forestry we need, as mentioned before, photography in a scale of 
1:20,000 and for forestry in some cases even a larger one. 
Thus we see that for systematic planning of air survey we must make use of two 
different coverages. Let us assume for the time being one coverage in about 1 : 75,000 and 
one in the scale 1 : 20,000. 
e. Combination of photography 1 : 20,000 with the small-scale photography. 
The planning organisation must determine these areas for which photography in the 
scale of 1 : 20,000 is also required, because this will in general not be for the whole area 
which is photographed in 1: 75,000. First we must know however, what further photo- 
grammetric production can be obtained from the photographs 1 : 20,000. It is obvious that 
this depends largely on the control and on the plotting equipment available. Maps in the 
scale 1 : 5,000 and even 2,500 can easily be derived from these photographs. This means 
that the same photography which is used for soil survey, can also be used for irrigation 
maps and for all kinds of geographical interpretation. It will, therefore, especially for 
this large-scale coverage, be desirable that the authority, responsible for the mapping 
project, enquires in advance of all government agencies dealing with related subjects, 
what their plans are for the near future. The result of this will be a project for special 
coverage 1 : 20,000 in addition to the general coverage 1 : 70,000. 
For those areas which will be photographed in the scale 1 : 20,000 we will not restrict 
ourselves to the plotting procedure described above, but carry out an aerial triangulation 
of the photographs 1 : 70,000 which will also provide the photographs 1 : 20,000 with 
control points. To this end it will be desirable that the coverages for the areas in common 
are obtained in the same season. 
A consequent solution in this respect would be to have two different cameras in the 
same aircraft in order to produce large and small-scale photography in one flight. The 
flying height should then be 6200 m which, in the super wide angle camera, gives a scale 
of 1 : 70,000, longitudinal overlap 80% and lateral overlap 30%. The second camera 
should be a normal angle one of the same 9 X 9 inch size and 12 inch principle distance; 
longitudinal overlap 60%, lateral overlap 22%, scale of photography 1 : 21,000. The super 
wide angle in this case needs only to take photographs in each 3rd strip.